Husband has hip pain when sitting or lying down but can walk miles without pain. Any ideas what this could be?? Arthritis??

While it is completley possible it could very well be other things. Has he had an injury to the area in the past? Did this come on all of a sudden out of nowhere?
Is the area hot and swollen?

Arthritis in the hip occurs over time and not instantanously so if the pain was sudden I would doubt that would be the case. Especially if the pain is only there when he lays down or sits. If you have it in the hip it hurts to stand up and walk.
It could be a number of things. It's possible there's some bursitis in the hip.
There is also the case it is his lumbar spine causing the pain and not his hip at all. This is quite common

His best bet is to start with the general practitioner and advise them of the symptoms, they will probably order an X-ray and possibly order some blood work to check SED rates and then advise you of which type of doctor he should see be it an Orthopeadist or a Rhuematologist

Barbie